Collocating Ceph volumes and instances in a multi-datacenter setup

OpenStack Havana is installed on machines rented from OVH and Hetzner. An aggregate is created for machines hosted at OVH and another for machines hosted at Hetzner. A Ceph cluster is created with a pool using disks from OVH and another pool using disks from Hetzner. A cinder backend is created for each Ceph pool. From the dashboard, an instance can be created in the OVH availability zone using a Ceph volume provided by the matching OVH pool.